Does δ<sup>18</sup>O of O<sub>2</sub> record meridional shifts in tropical rainfall?
Marine sediments, speleothems, paleo-lake elevations, and ice core methane and <i>δ</i><sup>18</sup>O of O<sub>2</sub> (<i>δ</i><sup>18</sup>O<sub>atm</sub>) records provide ample evidence for repeated abrupt meridional shift...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-10-01
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| Series: | Climate of the Past |
| Online Access: | https://www.clim-past.net/13/1323/2017/cp-13-1323-2017.pdf |
| Summary: | Marine sediments, speleothems, paleo-lake elevations, and ice core
methane and <i>δ</i><sup>18</sup>O of O<sub>2</sub>
(<i>δ</i><sup>18</sup>O<sub>atm</sub>) records provide ample evidence
for repeated abrupt meridional shifts in tropical rainfall belts
throughout the last glacial cycle. To improve understanding of the
impact of abrupt events on the global terrestrial biosphere, we
present composite records of <i>δ</i><sup>18</sup>O<sub>atm</sub> and
inferred changes in fractionation by the global terrestrial
biosphere (Δ<i>ε</i><sub>LAND</sub>) from discrete gas
measurements in the WAIS Divide (WD) and Siple Dome (SD) Antarctic
ice cores. On the common WD timescale, it is evident that maxima in
Δ<i>ε</i><sub>LAND</sub> are synchronous with or shortly
follow small-amplitude WD CH<sub>4</sub> peaks that occur within
Heinrich stadials 1, 2, 4, and 5 – periods of low atmospheric
CH<sub>4</sub> concentrations. These local CH<sub>4</sub> maxima have been
suggested as markers of abrupt climate responses to Heinrich
events. Based on our analysis of the modern seasonal cycle of gross
primary productivity (GPP)-weighted <i>δ</i><sup>18</sup>O of
terrestrial precipitation (the source water for atmospheric
O<sub>2</sub> production), we propose a simple mechanism by which
Δ<i>ε</i><sub>LAND</sub> tracks the centroid latitude of
terrestrial oxygen production. As intense rainfall and oxygen
production migrate northward, Δ<i>ε</i><sub>LAND</sub>
should decrease due to the underlying meridional gradient in
rainfall <i>δ</i><sup>18</sup>O. A southward shift should increase
Δ<i>ε</i><sub>LAND</sub>. Monsoon intensity also
influences <i>δ</i><sup>18</sup>O of precipitation, and although we
cannot determine the relative contributions of the two mechanisms,
both act in the same direction. Therefore, we suggest that abrupt
increases in Δ<i>ε</i><sub>LAND</sub> unambiguously imply
a southward shift of tropical rainfall. The exact magnitude of this
shift, however, remains under-constrained by Δ<i>ε</i><sub>LAND</sub>. |
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| ISSN: | 1814-9324 1814-9332 |